Question

A passenger train takes 1 hour less for a journey of 150km if it's speed is increased by 5kmph from its usual speed.find the usual speed of train.​

Answer 1

let x be speed of train & y be time taken by the train

so, distance=xy=150......(1)

​ according to question,

time taken will be 1hr less when speed is increased by 5kmph for the same distance as in (1)

so,

(x+5)(y-1)=xy

​xy-x+5y-5=xy

​-x+5y-5=0

substitute y=150/x ( from (1) )

so ,

-x+5(150/x)-5=0

on solving this quadratic eq, we get 2 values for x

they are,

x=25 or x=-30

x=-30 is rejected as speed can't be negative

so actual speed of train that is x=25 kmph